The present invention relates to a television signal determination circuit in an automatic tuning system which automatically tunes a television set to local channels.
It is customary to perform tuning operation in TV receivers while a viewer manually rotates a tuning knob. However, the tuning operation is bothersome in the case of the continuously varying tuning operation as in UHF reception. Though tuning operation is considerably simpler in the case of TV receivers of the recently developed touch control type or remote control type, it is considerably difficult for a non-skilled person to preset the tuner, or to adjust the tuning frequencies for respective broadcasting stations before starting to watch a TV receiver.
Various automatic tuning systems are proposed to simplify the preset tuning operation in TV receivers. However, there is a possibility that the automatic tuning system will erroneously respond to noises rather than desired television signals.
Accordingly, an object of the present invention is to stabilize tuning operation of an automatic tuning system.
Another object of the present invention is to provide a television signal determination circuit for determining whether the received signals are desired television signals.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a television signal determination circuit is provided for determining whether received signals are desired television signals. The television signal determination circuit, in a preferred form, comprises a first counter means for counting received synchronizing signals for a predetermined period of time, a second counter means for counting reference clock signals for the predetermined period of time and a determination means for determining whether the synchronizing signals are received by a predetermined number within the predetermined period of time by comparing output signals from the first and second counter means. When the synchronizing signals are received by the predetermined number within the precetermined period of time, the received signals are considered as the desired television signal.